1. Field of the Invention
The present invention relates to an energy dispersion type radiation detecting system and a method of measuring a content of an object element for irradiating an incident irradiation of an X-ray, an electron beam or the like to a sample, detecting a radiation of a characteristic X-ray generated from the sample and carrying out an element analysis and a composition analysis of the sample from a spectrum of the radiation.
2. Description of the Related Art
In a related art, as a method of carrying out an element analysis and a composition analysis of a sample, there is a method of irradiating an incidence radiation of an X-ray, or an electron beam from an incidence system to a sample constituting an object, detecting a radiation of a characteristic X-ray or the like generated by exciting an element contained in the sample by the incidence radiation by a detecting system to analyze. Further specifically, for example, when an electron beam is used as the incidence radiation, an electron beam is irradiated to a sample from an electron gun and a characteristic X-ray is detected as a radiation irradiated from the sample. Further, a content of an object element can be specified by detecting an intensity of the characteristic X-ray with regard to a desired object element by a spectrum of the characteristic X-ray. According to a method of specifying the content of the object element from a spectrum analysis of the irradiation irradiated from the sample by using a radiation detecting system having the incidence system and the detecting system, generally, by increasing an intensity of the incidence radiation from the incidence system, also the intensity of the radiation can be increased and a sensitivity can be increased. Therefore, an accurate measurement can be carried out by restraining a minimum limit of detection. Further, when an incidence radiation is constituted by an X-ray, a characteristic X-ray generated by exciting an element contained in a sample by the incidence radiation is referred to as a fluorescent X-ray.
On the other hand, when the intensity of the incidence radiation is increased to be equal to or larger than a predetermined intensity, the radiation is incident on a detection system of a radiation detecting system more than a detectable count number, and therefore, dead time during which the incident radiation cannot be detected is increased. Therefore, generally, an intensity of the incidence radiation is set to an intensity as high as possible within a range in which the dead time becomes 30% through 50%, and there is also proposed an apparatus of automatically setting an intensity of the radiation line such that the dead time falls in the range (refer to, for example, JP-A-5-258693).
Further, in recent years, in a radiation detecting system for detecting a radiation, a function of a detecting system or the like is remarkably promoted, whereas a detectable total counting rate is about 10 kps in a related art, the counting rate is increased up to 10 times through 50 times as much as the counting rate of the related art, and a radiation emitted from the sample can be detected by irradiating an incidence radiation having a higher intensity to a sample.
However, even when a radiation having a high intensity is irradiated in the range in which the dead time becomes 30% through 50% in accordance with an increase in the total counting rate of the detecting system, there poses a problem that the detecting system is significantly effected with an influence of pile up. As shown by FIG. 4, pile up is a phenomenon in which when a radiation incident on a detecting system to be counted is detected to process as a pulse signal 21, by overlappingly detecting other pulse signal 22, a height or a width of actually detected pulse signal is deformed as in a pulse signal 23. By generating the pile up, a nonlinear distortion is produced in a spectrum of a detected radiation, and an increase in a background intensity becomes significant. Therefore, there poses a problem that even when the incidence radiation is constituted by the high intensity within the range in which the dead time becomes 30% through 50%, as a result, a minimum limit of detection is increased and an accurate measurement cannot be carried out.